An initiative is under way to bolster navigation by cross-referencing in situ gravity measurements with a gravity map of Earth – information that could be used in conjunction with satellite data to determine ships’ positions more accurately.
The project will apply on Earth scientific principles best embodied on NASA’s InSight probe, currently on Mars. The device is using humanity’s best ever gravimetric sensor – the MEMS Seismometer – to listen for so-called ‘marsquakes’ at a sensitivity of 0.3 ng/rtHz*.
Combining GPS positioning data and localised gravity field measurements would significantly improve the reliability of navigation systems, allowing vessels to more accurately determine their location. The project has just secured GBP600,000 (USD768,000) in funding from the Partnership Resource Fund of the UK Quantum Technology Hub in Sensors and Timing, led by the University of Birmingham.
“This grant will help us transfer the technology we developed for Mars back to Earth, or more specifically onto our oceans,” said project leader Tom Pike, professor at Imperial College London, who developed the sensors on Mars InSight.
Nearly every form of today’s navigation, both on land and at sea, relies on satellite positioning data. However, these networks are vulnerable in various respects, according to a 2019 report by the UK Department of Transport. “A key problem that must be addressed in navigation safety terms is the overwhelming reliance on Global Navigation Satellite Systems with its inherent vulnerabilities to man-made interference and space weather,” the report noted. “There are numerous examples of accidents and incidents associated with navigation error.”
The greatest challenge involved in the project will be in creating a gravimetric sensor that can operate under acceleration of more than 0.1 g, since gravity sensors require extreme precision, detecting signals at the nano-g level. “We know we have the robustness to survive a trip to another planet,” said Pike. “Now we want to show we have the sensitivity to detect gravitational changes while rocking on a ship. It’s more of a challenge than detecting marsquakes!
“As far as I understand Mars is indeed not geologically active and more like a solid bell,” said Professor Kai Bongs, principal investigator at the UK Quantum Technology Hub in Sensors and Timing. “The quakes are consequently more like a ringing, after being hit by some space debris falling onto Mars.”
There are existing gravity maps of Earth, assembled by satellite gravimetry; the World Gravity Map 2012 (WGM2012) is one example. However, Bongs said, “A finely detailed Earth gravity map would still require some effort and investment.”
Putting together a complete and highly detailed gravimetric map would be similar to the way marine hydrography operates today, he explained. “The gravity map matching devices can start operating using existing large-scale maps, but also contribute to refining maps by feeding information back into map creation. It certainly can add to the various data sources used in hydrography and we hope it can improve best practice there, as well.
“We’re delighted with this opportunity to extend our cold atom quantum technology in map-matching navigation to maritime environments, using MEMS-enhanced technology developed by leading electronics expert Dr Simon Calcutt in a project led by Professor Tom Pike.”
* “This measurement means that it can measure accelerations of 300 trillionth of the Earth’s acceleration within one second, and the sensitivity increases with the square root of the measurement time,” Professor Bongs explained.